In conventional examples, a life of a polishing pad for use in polishing of a wafer becomes clear only after the wafer actually polished with this polishing pad is cleaned, then a plurality of quality items of the wafer are monitored with the use of an inspection apparatus, and occurrence of abnormality in any quality item is detected.
As one of the quality items, for example, LPD (Light Point Defects) representing cleanliness of a surface of a wafer is used. This LPD is measured by irradiating a surface of a wafer with a laser beam and condensing reflecting light therefrom. When a particle or a COP (Crystal Original Pit) is present on the surface of the wafer, the reflecting light is irregularly reflected, and this scattered light is condensed by a photodetector to detect presence of the particle or the COP. At this time, a diameter of the particle or the COP as a measurement target is preset, and the total number of particles or COPs whose diameters are equal to or higher than the set diameter is measured. When a measurement value of this LPD exceeds a reference value serving as acceptance and rejection criteria, the life of the polishing pad is determined to have reached an end (see Patent Literature 1).
FIG. 8 shows an example of a relationship between LPD of a wafer and a use time of a polishing pad after double-side polishing. An axis of ordinate of a graph represents a value (LPD/reference value) obtained by dividing a measurement value of the LPD by a reference value serving as the acceptance and rejection criteria, and an axis of abscissa represents a use time (min) of the polishing pad. It is to be noted that the LPD was measured for three times and, for each of three times, a plurality of silicon wafers each having a diameter of 300 mm were polished by a 4-way type double-side polishing machine, the polished silicon wafers were cleaned and dried, and then the LPD was measured by Surfscan SP1 manufactured by KLA-Tencor. At this time, the number of the LPD each having a diameter of 0.2 μm or more was counted. A polyurethane foam pad (LP-57 manufactured by JH RHDES) was used as a polishing pad, and KOH alkali base colloidal silica (GLANZOX2100 manufactured by Fujimi Incorporated) was used as slurry.
It is determined that a wafer is rejected when a value of (LPD/reference value) exceeds 1, and a life of the polishing has reached an end.